Treatment of clay-containing formations



Flare-12 3,236,306 TREATMENT OF CLAY-CONTAINING FORMATIONS Donald K.Atwood, Bellaire, T ex., assignor, by mesne assignments, to EssoProduction Research Company,

Houston, Tex., a corporation of Delaware No Drawing. Filed Nov. 7, 1963,Ser. No. 322,058 Claims. (Cl. 166-42) The present invention is directedto treatment of. subsurface clay-containing formations. Moreparticularly, the invention is concerned with treatment of subsurfaceclay-containing formations which have been contacted is also applicableto water injection wells, and the like.

In the practice of the present invention, the formation which has beencontacted with fresh water and the permeability thereof lowered by saidcontact is preferably treated first with a liquid hydrocarbon and thenwith an aliphatic alcohol in which water is soluble in an amount withinthe range from about 2.0% to about 12% by weight and which has aninterfacial tension with water of at least about 4 but which may rangeupwardly to about'10 dynes per cm. The partition coetlicient, which isthe ratio of the solubility of water in the alcohol to the solubility ofthe alcohol in water, must be at least about 3 and may range upwardly tothe maximum for the solubility in water which is about 1200. Thereafter,the formation is then treated again with a liquid hydrocarbon wherebythe original permeability of the forma tion is substantially restored.

The alcohols finding use in the present invention are preferably thenormal saturated aliphatic alcohols. H owever, the invention is notlimited to the normal saturated alcohols, but other alcohols may beemployed provided the alcohols have an interfacial tension with waterwithin the range of about 4 to 10 dynes per cm. and the solubility ofwater in the alcohol is from about 2.0% to about 12% by weight- In thepresent invention, water is soluble in the alcohol in an amount up toabout 12% by weight and has an interfacial tension with water in dynesper cm. at least about 4.0.

The alcohols which satisfythese requirements may be exemplified byl-pentanol, Z-pentanol, 3-pentancl, mix tures of isomeric pentanols,l-hexanoi, i-heptanol, loctanol and mixtures of isomeric isooctanols,2-ethylbutanol, Z-ethylhexanol, mixtures of isomeric decanols and2-methylpentanol. Of these alcohols, the pentanols, 2-hexanol andl-heptanol are preferred. For example, l-hexanol has an interfacialtension with water of 6.8 dynes per cm. and water is soluble in thealcohol to an extent of 7.2% by weight. 'In short, in the practice ofthe present invention the alcohol is only partially miscible or solublein water. The following table gives the we ttLl LMLHUL.

, aztases ?atented Feb. 22, 1965 characteristics of the alcohols whichmay be used in the present invention:

Table I Percent In ter- Solnby wt. Partition facial Alcohol bility,Water Coefll- Tension,

in Water lnelent dynes] n-Butanol 7. 7 20. t 2. 6 1. 8 Isobntnnol 8. 715. 0 .l. 7 2. 1 1-Pentun0l. 2. 7 10. 2 3. 8 4. Q B-Pentanol.-- 2.0 8. 34. 1 4. 5 Mixed Isom rs 1. 7 9. 2 5. 4 4. 4 l-Hexnnol.-. 0. 6 7. 2 12. 40. 8 1-Heptanol 1. 8 5. 4 3. 0 7. 7 Octnnol-mixed isomers- 0. l 3. 5 35.0 7. 7 Z-Hthylbutanol 0. 4 4. 6 12. 5 7. 5 2-Etliylhexanol 0.1 2.6 26.09.0 2-Methylpcntanol 0.3 6. 4 38. 0 6. 0 Mixed isomers-Decanol 01 2. 4240. 0 8. v5

alcohol. The interfacial tension may be measured by any standard meanssuch as the drop-weight method or with a du Nouy tensiometer. Thismeasurement is made at the interface between the two liquid phases, eachsaturated with the other.

The amount of alcohol to be employed in the practice of the presentinvention may range from about 42 to about 84 gallons of alcohol perfoot of formation to be treated. Stating this otherwise, a volume ofalcohol equivalent to about 1 to about 2 times the pore volume of theportion of formation to be treated may be sufficient.

The hydrocarbon employed in the practice of the present invention is aliquid hydrocarbon such as one having a' viscosity from about 0.5 toabout 5.0 centipoises at F. Exemplary of the liquid hydrocarbons may bementioned the gasoline hydrocarbons boiling from about F. up to about400 F. and fractions thereof, kerosene, gas-oil and fractions ofkerosene and gas-oil. Purified hydrocarbons may also be employed suchas, but not restricted to pentane, hexane, heptane, octane, the othermembers of the homologous series, as well as the correspondingnaphthenic and aromatic hydrocarbons. In the practice of the presentinvention, hydrocarbons having viscosities in the range given boilingfrom about 80 F. up to about 750 F. may be used. The lower boilinghydrocarbons may also be employed provided a pressure is employedsullicient to maintain the normally gaseous hydrocarbons in the liquidphase.

' The amount of hydrocarbons employed may range from about to aboutgallons per foot of formation which is contacted with the hydrocarbon.Stating the quantity of the hydrocarbon differently, the total volume ofhydrocarbon may be equivalent to about i to about 3 times the porevolume. The hydrocarbon application will be preferably applied beforeand after the treatment with the alcohol although either or both of thehydrocarbon treatments may be dispensed with under certain circumlevy...

J stances. This treatment may be applied, as stated, before and afterthe treatment with the alcohol and may be divided equally; an amountwithin the range of about 40% to about 60% may be applied before alcoholtreatment and then an amount within the range of about 40% to about 60%may be applied after alcohol treatment.

In treating a formation in accordance with the present invention, anamount of hydrocarbon within the range stated will be introduced into awell bore drilled to pierce the formation which is to be treated andwhich has been damaged by contact with fresh water, followed by thestated amount of alcohol which is then followed by the treatment with anadditional amount of hydrocarbon. A sufiicient pressure below thefracture gradient of the formation may be applied to force thehydrocarbon, alcohol, and hydrocarbon into the formation. Thereafter,the pressure may be reduced and hydrocarbons produced from the formationsince the permeability of the formation is restored by the practice ofthe present invention.

In this connection, it has been found that sharp reductions inpermeability often occur when relatively fresh water contactsclay-containing formations during drilling and workover operations. Thecommon clay minerals which are known to cause permeability damage toformations are montmorillonites, kaloins, chlorites and illites. Theseclays are constructed of particles which adsorb water on their surfaceand edges. This adsorption increases as water salinity decreases, and atlow salinity, particles disperse into'the aqueous phase. Permeabilitylosses are caused by removal of inorganic ions from the environmentsurrounding the clay with consequent swelling and/or dispersion of clayminerals into the pore space. This phenomenon is generally termed claydamage, fresh water damage, or simply formation damage, and it causeslarge loss in current revenue by preventing oil wells from making theirallowable production. Heretofore, no satisfactory method existed forrestoring permeability to claycontaining formations damaged by water.With the practice of the present invention, losses of permeabilitysuffered by contacting the formation with fresh water are substantiallyrestored or, in some instances, the permeability is increased. Inaccordance with the present invention, by treatment of the water-damagedformation with an alcohol of the type set out herein, permeability issubstantially restored to the formation.

In order to illustrate the present invention further, a number of runswere made on core plugs cut from well cores containing clay. These coreplugs were deliberately damaged with fresh water and then attempts weremade to restore the permeability or repair the damage.

' To this end, a 1-inch core plug is cut from conventional well corescontaining clay. These core plugs are extracted with tetrachloroethyleneto remove hydrocarbons, and with methanol to remove water. Afterextraction, the cores are saturated with 12% sodium chloride solutionand confined in the rubber sleeve of a permeability apparatus at apressure of 300 p.s.i.g. Fluids are then flowed through the cores inaccordance with the following flood sequence:

(1) 12% sodium chloride solution.

(2) Kerosene having a viscosity of 2.6 centipoises. (3) Fresh water.

(4) Kerosene having a viscosity of 2.6 centipoises. (5) Treating agent.

(6) Kerosene having a viscosity of 2.6 centipoises.

In a first run using the sequence set out above, oil permeability ofcores is measured before and after damage by fresh water. Comparison ofthe permeabiiities shows that each core is badly damaged by fresh water.Acetone is then flooded through the cores until most of the water isextracted from the pore space. The cores are then flooded with keroseneand permeabilities are measured for comparison with the damagedpermeability.

In one of the cores, the permeability is increased only slightly, whilein the other, it is actually decreased to a value well below the freshwater damaged permeability. Vacuum distillation of the cores uponcompletion of the last oil flood shows that the water saturation isreduced by the acetone flood to less than 10% of the pore volume or porecores.

In another operation, runs identical to those performed with acetone aremade using isopropyl alcohol as the treating agent. Again, in thisinstance the increase in permeability is small compared to the loss inpermeability when the core is damaged by contact with fresh water.Vacuum distillation after final oil floods reveals that water saturationis well below 10% of the pore volume.

Other operations are conducted with ethanol in runs identical to thosedescribed for acetone and isopropyl alcohol. Permeabilitles measuredduring the early stages of the final oil flood are essentially the sameas the damaged permeability even though subsequent vacuum distillationindicates that the water saturation has been drastically reduced. As theoil fiood'continues, the permeability gradually increased but the finalvalue is still well below the original permeability.

In accordance with the present invention, operations were performedwhere normal l-hexanol was employed as the treating agent. The resultsof these runs are set out in the following Table ll.

Table II EFFECT OF n-HEXANOL ON DAMAGED CORES General Flood SequenceCore Core Core Core Core Com 1. k. to 12% N801 solu 17 a4 0. can 1. of1st 200 2. [Co to Kerosenm 1.- 0. 05 Tl U. 243 ll. 17 199 107 3. k. todistilled ll O- 3X10 1 iZXllH 2. 35 0. 60 4. its to Kerosene. 0. 50 4 U.202 158 57 5. Inject. n-Hoxnnol. t5. ks to Kerosene alt.

n-Hoxallol l. 6 55 0. 381 S. 250 253 Percent montmorillonite. 810 68 6-87-9 7-10 1 k' is permeability to water in mlllldarclcs. kt. ispermeability to oil in mlllldarcies.

From the foregoing data, it will be clear that the treatment with normalhexanol restored the permeability to kerosene of each core and actuallyincreased the permeability of some cores. in short, the presentinvention allows the obtaining of unobvious resuits over the treatmentwith water-miscible solvents such as acetone, isopropyl alcohol andethanol.

Runs are made employing l-pentanol, l-heptanol. and l-hcxanol, using thesequence of treatment outlined heretotore. in each of these instances,the permeability of the water-damaged, clay-containing formation issubstantially restored.

Similar treatments are performed with other alcohols such as isomericoctanols, Z-ethylhexanol and isomeric decanols. The improvedpcrmeabilities are also obtamed.

The present invention is quite advantageous and useful in thatrestoration of permeability to water-damaged formations allows increasedproduction of hydrocarbons to be obtained from the damaged formations.Thus, the present invention is quite advantageous and useful.

The nature and objects of the present invention having been completelydescribed and illustrated and the best mode thereof contemplated setforth, what we wish to claim as new and useful and secure by LettersPatent is:

1. A method for treating a subsurface clay-containing formation whichhas been damaged by contact with fresh water such that the permeabilityof said formation has been lowered which comprises treating said damagedformation with an aliphatic alcohol in which water is soluble in anamount from about 2% to about 12% by weight and which has an interfacialtension with water in dynes per cm. at least about 4.0 and a partitioncoetticient at least about 3 whereby the original penneability of saidformation is substantially restored.

2. A method in accordance with claim 1 in which the alcohol is pentanol.

3. A method in accordance with claim 1 in which the alcohol isl-hexanol.

4. A method in accordance with claim 1 in which the alcohol isl-heptanol.

5. A method in accordance with claim 1 in which the interfaci'al tensionwith water is within the range from about 4 to about dynes per cm.

6. A method for treating a subsurface clay-containing formation piercedby a well, said formation having been damaged by contact with freshwater such that the permeability of said formation has been lowered,which comprises injecting into said well an aliphatic alcohol in whichwater is soluble in an amount from about 2% to about 12% by weight andwhich has an interfacial tension with water in dynes per cm. at leastabout 4.0 and a partition coeflicient of at least 3 and treating anexposed face of said formation with said alcohol whereby the originalpermeability of said formation is substantially restored.

7. A method in accordance with'claim 6 in which the alcohol is pentanol.

8. A method in accordance with claim 6 in which the alcohol is1-hexanol.

9. A method in accordance with claim 6 in which the alcohol isl-heptanol. l

10. A method for treating a subsurface clay-containing formation piercedby a well, said formation having been damaged with fresh water such thatthe permeability of- 6 a partition coefficient of at least 3, and thencontacting the treated formation with a liquid hydrocarbon whereby theoriginal permeability of siad formation is substantially restored.

11. A method in accordance with claim 10in which the hydrocarbon iskerosene.

Q the alcohol is hexanol.

13. A method for treating ,a subsurface clay-containing formationpierced by a well, said formation having been damaged with fresh watersuch that the permeability of said formation has been lowered, whichcomprises first contacting said damaged formation with a liquidhydrocarbon, treating said first contacted formation with an aliphaticalcohol in which water is soluble in an amount from about 2% to about12% by weight and has an interfacial tension with water in dynes per cm.at least about 4.0 and a partition coeflicient of at least 3, and thencontacting the treated formation with a liquid hydrocarbon whereby theoriginal permeability of said formation is substantially restored.

14. A method in accordance with claim 13 in which the hydrocarbon iskerosene.

15. A method in accordance with claim 14 in which the alcohol isl-hexanol.

References Cited by the Examiner UNITED STATES PATENTS 2,324,254 7/ 1943Bertness et a1, 166-44 2,345,713 4/ 1944 Moore et a1. 166-42 3,036,6305/1952 Bernard et al. l6642 X CHARLES E. OCONNELL, Primary Examiner.

EDWARD M.. FLETCHER, IR.

UNI'IEDSTATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,236,306 February 22, 1966 Donald K. Atwood It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 1, line 59, for "Z-hexanol" read l-hexanol Signed and sealed this23rd day of May 1967.

(SEAL) Attest:

Commissioner of Patents Attesting Officer EDWAIIFDNJ. BRENNER

1. A METHOD FOR TREATING A SUBSURFACE CLAY-CONTAINING FORMATION WHICHHAS BEEN DAMAGED BY CONTACT WITH FRESH WATER SUCH THAT THE PERMEABILITYOF SAID FORMATION HAS BEEN LOWERED WHICH COMPRISES TREATING SAID DAMAGEDFORMATION WITH AN ALIPHATIC ALCOHOL IN WHICH WATER IS SOLUBLE IN ANAMOUNT FROM ABOUT 2% TO ABOUT 12% BY WEIGHT AND WHICH HAS AN INTERFACIALTENSION WITH WATER IN DYNES PER CM. AT LEAST ABOUT 4.0 AND A PARTITIONCOEFFICIENT AT LEAST ABOUT 3 WHEREBY THE ORIGINAL PERMEABILITY OF SAIDFORMATION IS SUBSTANTIALLY RESTORED.